Patterns in Inherited Traits Chapter 13 Alleles and

Patterns in Inherited Traits Chapter 13

Alleles and Traits • Blending inheritance • Example: Black and white horse will produce _____offspring • Failed to explain how traits disappear over several generations and then _________unaltered generations later • Charles Darwin did not accept this idea • Gregor Mendel (__________) • Started breeding thousands of ____________ • Kept detailed record of how traits passed from one __________to the next • Began to formulate how _________works

Mendel’s Experiments • Garden pea plant is ____-fertilizing • The flowers produce male and female _______ • The experiments • Controlled the pairings between individuals, by removing __________, with specific traits and observed traits of their ____________ • _______fertilized plants and collected _______ • Recorded traits of new pea plants

Mendel’s Experiments • Started with garden pea plants that “bred true” for a particular trait _________________________ • Cross-fertilized pea plants with different traits and offspring appeared in __________________ • Concluded (correctly) that hereditary information is passed in discrete units

Inheritance in modern terms • Locus: ________________________ • Homozygous: ______________________ • Heterozygous: ______________________ • Hybrids are _______offspring of a cross between individuals that breed true for different forms of a trait • Dominant: Effect masks that of a recessive allele paired with it • represented by italic _______letters • Recessive: Effect is masked by a dominant allele paired with it • represented by italic ___________letters • Genotype: _______________________ • Phenotype: _________________

Allele distribution into gametes • A homozygous dominant pea plant with two alleles (____) has purple flowers, and a homozygous recessive pea plant with two alleles (___) has white flowers • If these _______plants are crossed (PP × pp), all offspring will be ___________ • All __________(F 1) offspring will be heterozygous • Genotype = _______ • Phenotype = _____________

DNA replication meiosis I 2 1 meiosis II 3 gametes (P) gametes (p) zygote (Pp)

Punnet square • A grid used to predict the _______ and _________ outcome of a cross male gametes female gametes

Testcross • _________________________ • An individual that has a dominant trait (but an unknown genotype [PP/Pp]) is crossed with one that is homozygous recessive_____ • Results?

Monohybrid cross • Breeding experiment in which individuals identically __________for _______gene are crossed (Pp×Pp) • Frequency of traits among offspring in the ________ offers information about the dominance relationship between the alleles • First generation = _______ • Second generation = ____ • Results? (Ratio, %)

Mendel’s Seven Pea Plant Traits

Monohybrid cross • https: //www. youtube. com/watch? v=EYYc 7 z 4 y. X 38

Law of segregation • The 3: 1 phenotype ratios in F 2 offspring of monohybrid crosses became the basis of ______________ • _______cells carry pairs of genes on each pair of _________________ • The two genes of each pair are _______from each other during meiosis so that they end up on ______ gametes

Dihybrid cross • Individuals __________for alleles of _______genes (dihybrids) are crossed, and the traits of the offspring are observed • Frequency of traits among the _______offers information about the ______relationships between the paired alleles

Dihybrid cross • One parent plant that breeds true for purple flowers and tall stems (______) is crossed with one that breeds true for white flowers and short stems (____) • Each plant makes only one type of gamete (____) • All F 1 offspring will be dihybrids (____) and have purple flowers and tall stems Punnett square • PT×pt

Dihybrid cross • The result of two F 1 plants crossing: a dihybrid cross (Pp. Tt × Pp. Tt) • Four types of gametes can combine in sixteen possible ways Punnett square

Dihybrid cross • In F 2 plants, four phenotypes result in a ratio of ______ • • _________________________________ • Go back and check results!

Law of Independent Assortment • Mendel discovered the 9: 3: 3: 1 ratio in his dihybrid experiments • Each trait still kept its individual 3: 1 ratio • Each trait sorted into gametes _______of other traits • During meiosis, members of a pair of genes on homologous chromosomes get distributed into gametes independently of other gene pairs

Contribution of Crossovers • How two genes get sorted into gametes depends on if they are found on same chromosome • Random assortment • Genes on one chromosome assort into gametes independent of genes on other chromosomes • Linkage group – all genes on a chromosome • Genes that are far apart on a chromosome tend to assort into gametes independently • Genes very close together on a chromosome are linked • They do not assort independently because crossing over rarely happens between them

Patterns of Inheritance • Simple/Complete dominance • A dominant allele fully masks the expression of a recessive one • Other patterns of inheritance are not so simple: • • Codominance Incomplete dominance Epistasis Pleiotropy

Codominance • Two alleles that are both fully expressed in heterozygous individuals • Multiple allele systems – gene for which three or more alleles persist in a population • Example: an ABO gene for blood type, human hair/eye color.

Codominance • Which two of the three alleles of the ABO gene you have determines your blood type • The A and the B allele are codominant when paired • Genotype AB = blood type AB • The O allele is recessive when paired with either A or B • Genotype AA or AO = blood type A • Genotype BB or BO= blood type B • Genotype OO = blood type O

Genotype: AA or AO Phenotype: A AB BB or BO OO AB B O

Incomplete dominance • One allele is not fully dominant over another • The heterozygous phenotype is between the two homozygous phenotypes (example: red×white=pink) • In snapdragons, one allele (R) encodes an enzyme that makes a red pigment, and allele (r) makes no pigment • RR = red; Rr = pink; rr = white • A cross between two pink (Rr × Rr) yields red, pink, and white in a 1: 2: 1 ratio

Epistasis • The effect in which a trait is influenced by the products of multiple genes • Example: Fur color in dogs • B=_____, b=______ • E=colour in fur, e=reduced colour in fur

Pleiotropy • _________________________ • Mutations in pleiotropic genes are associated with complex genetic disorders • Sickle-cell anaemia: a severe hereditary form of anemia (deficiency of red blood cells) in which a mutated form of ________distorts the red blood cells into a crescent shape at low oxygen levels • Cystic fibrosis: a hereditary disorder affecting the ________. It causes the production of abnormally thick _____, leading to the blockage of the pancreatic ducts, intestines, and bronchi and often resulting in ____________. • Marfan syndrome: a hereditary disorder of __________, resulting in abnormally long and thin digits and also frequently in optical and cardiovascular defects

Environment and Phenotype • Epigenetic research is revealing that environment can influence phenotype • Some examples of environmental effects • • _______________________________ ____________

Short tandem repeats • Some genes have regions of DNA in which a series of two to six nucleotides is repeated hundreds or thousands of times in a row • Example: 12 alleles of homeotic gene that influence face length in dogs • __________________________

Continuous variation • Some traits appear in two or three forms • Example: _____________________ • Others occur in a range of small differences • Example: _____________________ • The more genes and environmental factors that influence a trait, the more continuous the variation • If a trait varies continuously, it will have ________ curve

Cystic fibrosis • Most common fatal genetic disorder in the U. S. • Most CF patients live no more than ________ • The CFTR gene encodes a protein • Protein moves chloride ions out of ____________ • Binds disease-causing bacteria • Occurs in people _________for a mutated allele of CFTR gene (___________) • The allele of CF has a 3 base pair deletion • Called ΔF 508 because protein is missing the normal 508 th amino acid • People with CF inherit 2 copies of ΔF 508 • The deletion causes mucus to accumulate, making breathing difficult